With all the time he's had to prepare since 2008 when he last ran for president, you might have thought Mitt Romney would have come up with a more persuasive and sympathetic defense to the charge that illegal immigrants once worked on his Massachusetts property.

And with all the news coverage that issue got during the 2008 presidential campaign, including being raised in GOP debates, you might have also thought that Texas Gov. Rick Perry would have resorted to the story sooner to put Romney on the defensive and counter Romney's immigration attacks on him.

It took Perry until his fourth debate, however, to hit the former Massachusetts governor with it.

But politics, like the world itself, isn't always so straightforward.

So what happened Tuesday evening, in one of the most electric moments of the Republican debate in Las Vegas was Perry, at long last, unleashing on Romney. He accused his rival for the nomination of having "hired" undocumented workers to work on his Massachusetts property.

Defending himself as the two men talked over each other, barely able to contain their mutual dislike, the former Massachusetts governor hung onto the technical point that he hadn't hired the illegal workers himself.

True, the Boston Globe story that was the basis of Perry's charge didn't report that Romney himself had hired the undocumented workers; he used a landscaping contractor who had illegal workers on his crew.

A year after Romney learned this was so, however, the contractor was still sending undocumented workers to Romney's property in Belmont, Mass. When the Boston Globe again pointed this out, Romney fired the contractor. PolitiFact.com laid out the circumstances in a 2007 fact check.

While Romney was clearly ready for Perry's attack, part of his response to Perry may have only created additional problems for Romney. The former Massachusetts governor gave an answer that to many observers sounded cynical, conniving and morally relativistic.

That was just the kind of answer you don't want to give if you're a politician many voters have doubts about because they believe you're cynical, conniving and morally relativistic.

Here's part of Romney's exchange with Perry:

ROMNEY: So we went to the company and we said, look, you can't have any illegals working on our property. I'm running for office, for Pete's sake, I can't have illegals. It turns out that once again they had hired someone who had falsified their documents, had documents, and therefore we fired them. And let me tell you, it is hard in this country as an individual homeowner to know if people who are contractors working at your home, if they have hired people that are illegal. If I'm president, we'll put in an E-Verify system, which you have opposed —

COOPER: Out of time.

ROMNEY: — to make sure that we can find out who's here illegally and not, and crack down on people who come here illegally.

That "I'm running for office, for Pete's sake, I can't have illegals" threatens to haunt Romney through the remainder of the primary campaign season and beyond if he gets the nomination. It was a gaffe forced by Perry's aggressive use of the issue.

Which makes it fascinating that Perry didn't use this bit of Romney's past earlier, especially when Romney was pummeling him for supporting in-state college tuition in Texas for young undocumented immigrants.

In the era of Twitter and other social media where opposition research is crowdsourced, the information that Perry used to put Romney on the defensive on immigration was readily available.

Of course, it's the kind of charge a candidate like Perry would presumably want to make sure he himself wasn't vulnerable to before using it.

What good would it do to expose your opponent's problem with undocumented individuals working on his property only to have someone point out that you, too, had hired a contractor who brought illegal workers to your home? Or that you had directly hired illegal workers.

In a border state like Texas with its large population of undocumented workers, that would presumably be a fairly common experience that would be awfully hard to avoid.

So it would make sense for a campaign wanting to exploit the undocumented worker charge to make sure its own candidate didn't have an undocumented worker problem before attacking a rival candidate on the issue.

One thing is certain. We haven't heard the last on the issue of the undocumented workers who once worked on the Romney property.

And just as certain, there's someone out there who doesn't want to see Perry as the Republican presidential nominee, maybe working on Romney's behalf but not necessarily, who at this very moment is trying to determine if Perry has his own undocumented-worker problem, too.